Gyroxin is a thrombin-like enzyme present on L. muta venom and we purified this protein using an ecotin-affinity column. Ecotin is a serine protease inhibitor purified from E. coli that has been recently well characterized as a potent inhibitor of trypsin and related serine proteases. Ecotin is also able to inhibit the catalytic activity of gyroxin and its mechanism of interaction is still unknown. In order to study gyroxin' structure and its interaction with ecotin, we are using several multiple alignment programs at the Computer Graphics Laboratory to compare this protein from snake venom with homologous structures that have been described in the Brookhaven Protein Database. Initially, we were investigating its structural similarity with trypsin, trypsinogen and thrombin using the Blast program. We are using the known structures of these serine proteases to locate key determinants to ecotin binding in gyroxin.